The discussion below is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.
Small computing devices such as personal digital assistants (PDA), devices and portable phones are used with ever increasing frequency by people in their day-to-day activities. With the increase in processing power now available for microprocessors used to run these devices, the functionality of these devices is increasing, and in some cases, merging. For instance, many portable phones now can be used to access and browse the Internet as well as can be used to store personal information such as addresses, phone numbers and the like. Likewise, PDAs and other forms of computing devices are being designed to function as a telephone.
In many instances, mobile phones, PDAs and the like are increasingly being used in situations that require hands-free communication, which generally places the microphone assembly in a less than optimal position when in use. For instance, the microphone assembly can be incorporated in the housing of the phone or PDA. However, if the user is operating the device in a hands-free mode, the device is usually spaced significantly away from and not directly in front of the user's mouth. Environment or ambient noise can be significant relative to the user's speech in this less than optimal position. Stated another way, a low signal-to-noise ratio (SNR) is present for the captured speech. In view that mobile devices are commonly used in noisy environments, a low SNR is clearly undesirable.
To address this problem, at least in part, mobile phones and other devices can also be operated using a headset worn by the user. The headset includes a microphone and is connected either by wire or wirelessly to the device. For reasons of comfort, convenience and style, most users prefer headset designs that are compact and lightweight. Typically, these designs require the microphone to be located at some distance from the user's mouth, for example, alongside the user's head. This positioning again is suboptimal, and when compared to a well-placed, close-talking microphone, again yields a significant decrease in the SNR of the captured speech signal when compared to an optimal position.
One way to improve sound capture performance, with or without a headset, is to capture the speech signal using multiple microphones configured as an array. Microphone array processing improves the SNR by spatially filtering the sound field, in essence pointing the array toward the signal of interest, which improves overall directivity. However, noise reduction of the signal after the microphone array is still necessary and has had limited success with current signal processing algorithms.